RFC 7698

5. Control-Plane Requirements
The control of flexi-grid networks places additional requirements on
the GMPLS protocols. This section summarizes those requirements for
signaling and routing.
5.1. Support for Media Channels
The control plane SHALL be able to support media channels,
characterized by a single frequency slot. The representation of the
media channel in the GMPLS control plane is the so-called "flexi-grid
LSP". Since network media channels are media channels, an LSP may

also be the control-plane representation of a network media channel.
Consequently, the control plane will also be able to support network
media channels.
5.1.1. Signaling
The signaling procedure SHALL be able to configure the nominal
central frequency (n) of a flexi-grid LSP.
The signaling procedure SHALL allow a flexible range of values for
the frequency slot width (m) parameter. Specifically, the control
plane SHALL allow setting up a media channel with frequency slot
width (m) ranging from a minimum of m = 1 (12.5 GHz) to a maximum of
the entire C-band (the wavelength range 1530 nm to 1565 nm, which
corresponds to the amplification range of erbium-doped fiber
amplifiers) with a slot width granularity of 12.5 GHz.
The signaling procedure SHALL be able to configure the minimum width
(m) of a flexi-grid LSP. In addition, the signaling procedure SHALL
be able to configure local frequency slots.
The control-plane architecture SHOULD allow for the support of the
L-band (the wavelength range 1565 nm to 1625 nm) and the S-band (the
wavelength range 1460 nm to 1530 nm).
The signaling process SHALL be able to collect the local frequency
slot assigned at each link along the path.
The signaling procedures SHALL support all of the RSA architectural
models (R&SA, R+SA, and R+DSA) within a single set of protocol
objects, although some objects may only be applicable within one of
the models.
5.1.2. Routing
The routing protocol will support all functions described in
[RFC4202] and extend them to a flexi-grid data plane.
The routing protocol SHALL distribute sufficient information to
compute paths to enable the signaling procedure to establish LSPs as
described in the previous sections. This includes, at a minimum, the
data described by the information model in Figure 17.
The routing protocol SHALL update its advertisements of available
resources and capabilities as the usage of resources in the network
varies with the establishment or teardown of LSPs. These updates
SHOULD be amenable to damping and thresholds as in other traffic
engineering routing advertisements.

The routing protocol SHALL support all of the RSA architectural
models (R&SA, R+SA, and R+DSA) without any configuration or change of
behavior. Thus, the routing protocols SHALL be agnostic to the
computation and signaling model that is in use.
5.2. Support for Media Channel Resizing
The signaling procedures SHALL allow the resizing (growing or
shrinking) of the frequency slot width of a media channel or network
media channel. The resizing MAY imply resizing the local frequency
slots along the path of the flexi-grid LSP.
The routing protocol SHALL update its advertisements of available
resources and capabilities as the usage of resources in the network
varies with the resizing of LSPs. These updates SHOULD be amenable
to damping and thresholds as in other traffic engineering routing
advertisements.
5.3. Support for Logical Associations of Multiple Media Channels
A set of media channels can be used to transport signals that have a
logical association between them. The control-plane architecture
SHOULD allow multiple media channels to be logically associated. The
control plane SHOULD allow the co-routing of a set of media channels
that are logically associated.
5.4. Support for Composite Media Channels
As described in Sections 3.2.5 and 4.3, a media channel may be
composed of multiple network media channels.
The signaling procedures SHOULD include support for signaling a
single control-plane LSP that includes information about multiple
network media channels that will comprise the single compound media
channel.
The signaling procedures SHOULD include a mechanism to associate
separately signaled control-plane LSPs so that the endpoints may
correlate them into a single compound media channel.
The signaling procedures MAY include a mechanism to dynamically vary
the composition of a composite media channel by allowing network
media channels to be added to or removed from the whole.
The routing protocols MUST provide sufficient information for the
computation of paths and slots for composite media channels using any
of the three RSA architectural models (R&SA, R+SA, and R+DSA).

5.5. Support for Neighbor Discovery and Link Property Correlation
The control plane MAY include support for neighbor discovery such
that a flexi-grid network can be constructed in a "plug-and-play"
manner. Note, however, that in common operational practice,
validation processes are used rather than automatic discovery.
The control plane SHOULD allow the nodes at opposite ends of a link
to correlate the properties that they will apply to the link. Such a
correlation SHOULD include at least the identities of the nodes and
the identities that they apply to the link. Other properties, such
as the link characteristics described for the routing information
model in Figure 17, SHOULD also be correlated.
Such neighbor discovery and link property correlation, if provided,
MUST be able to operate in both an out-of-band and an out-of-fiber
control channel.
6. Security Considerations
The control-plane and data-plane aspects of a flexi-grid system are
fundamentally the same as a fixed-grid system, and there is no
substantial reason to expect the security considerations to be any
different.
A good overview of the security considerations for a GMPLS-based
control plane can be found in [RFC5920].
[RFC6163] includes a section describing security considerations for
WSON, and it is reasonable to infer that these considerations apply
and may be exacerbated in a flexi-grid SSON system. In particular,
the detailed and granular information describing a flexi-grid network
and the capabilities of nodes in that network could put stress on the
routing protocol or the out-of-band control channel used by the
protocol. An attacker might be able to cause small variations in the
use of the network or the available resources (perhaps by modifying
the environment of a fiber) and so trigger the routing protocol to
make new flooding announcements. This situation is explicitly
mitigated in the requirements for the routing protocol extensions
where it is noted that the protocol must include damping and
configurable thresholds as already exist in the core GMPLS routing
protocols.

7. Manageability Considerations
GMPLS systems already contain a number of management tools:
o MIB modules exist to model the control-plane protocols and the
network elements [RFC4802] [RFC4803], and there is early work to
provide similar access through YANG. The features described in
these models are currently designed to represent fixed-label
technologies such as optical networks using the fixed grid;
extensions may be needed in order to represent bandwidth,
frequency slots, and effective frequency slots in flexi-grid
networks.
o There are protocol extensions within GMPLS signaling to allow
control-plane systems to report the presence of faults that affect
LSPs [RFC4783], although it must be carefully noted that these
mechanisms do not constitute an alarm mechanism that could be used
to rapidly propagate information about faults in a way that would
allow the data plane to perform protection switching. These
mechanisms could easily be enhanced with the addition of
technology-specific reason codes if any are needed.
o The GMPLS protocols, themselves, already include fault detection
and recovery mechanisms (such as the PathErr and Notify messages
in RSVP-TE signaling as used by GMPLS [RFC3473]). It is not
anticipated that these mechanisms will need enhancement to support
flexi-grid, although additional reason codes may be needed to
describe technology-specific error cases.
o [RFC7260] describes a framework for the control and configuration
of data-plane Operations, Administration, and Maintenance (OAM).
It would not be appropriate for the IETF to define or describe
data-plane OAM for optical systems, but the framework described in
RFC 7260 could be used (with minor protocol extensions) to enable
data-plane OAM that has been defined by the originators of the
flexi-grid data-plane technology (the ITU-T).
o The Link Management Protocol (LMP) [RFC4204] is designed to allow
the two ends of a network link to coordinate and confirm the
configuration and capabilities that they will apply to the link.
LMP is particularly applicable to optical links, where the
characteristics of the network devices may considerably affect how
the link is used and where misconfiguration or mis-fibering could
make physical interoperability impossible. LMP could easily be
extended to collect and report information between the endpoints
of links in a flexi-grid network.